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  Java Practices -> Assertions in general
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<div class='page-title'>Assertions in general</div>

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<br><a href="http://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html">Assertions</a>
in general :
<ul>
<li>
when an assertion is fired, <a href="TopicAction3af3-2.html">pass the offending piece
of data</a> to <tt><a href="http://java.sun.com/javase/6/docs/api/java/lang/AssertionError.html">AssertionError</a></tt></li>

<li>
the checks performed inside an assertion are usually simple boolean conditions
- side effects are usually to be avoided</li>

<li>
since assertions can be disabled, the behaviour of a program must not depend
upon assertions being executed</li>

<li>
if desired, the <a href="TopicActionc981-2.html">conditional compilation</a> idiom
can still be used</li>

<li>
you can almost always ignore the methods in <tt><a href="http://java.sun.com/javase/6/docs/api/java/lang/ClassLoader.html">ClassLoader</a></tt> regarding
assertions - they are intended for interpreters such as <tt>java</tt>,
and are not used in a typical program</li>
</ul>
Reminders regarding use :
<ul>
<li>
to compile code containing assertions, older JDKs need to add <tt>-source 1.4</tt> as a command
line argument to <tt>javac</tt></li>

<li>
at runtime, assertions are disabled by default</li>

<li>
the <tt>-enableassertions</tt>&nbsp; and <tt>-disableassertions</tt> 
<a href="http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html#standard" title="Standard options for java interpreter">runtime parameters</a> 
(or their synonyms <tt>-ea</tt> and <tt>-da</tt>) control assertions
to any degree of&nbsp; granularity</li>

<li>
<tt><a href="http://java.sun.com/javase/6/docs/api/java/lang/AssertionError.html">AssertionError</a></tt> behaves as any other <tt>Error</tt>, and is not
affected by enabling or disabling of assertions.</li>
</ul>
Examples of typical styles, which affect non-system classes :
<br>&nbsp;
<table BORDER WIDTH="100%" border='1' cellspacing='0' cellpadding='3'>
<tr>
<th>Runtime command line</th>

<th>Classes with assertions enabled</th>
</tr>

<tr>
<td>java -ea&nbsp; Main</td>

<td>all classes</td>
</tr>

<tr>
<td>java -ea:com.Blah&nbsp;&nbsp; Main</td>

<td>one particular class named <tt>Blah</tt></td>
</tr>

<tr>
<td>java -ea:com.data... Main</td>

<td>all classes in the com.data package, and all of its sub packages</td>
</tr>

<tr>
<td>java -ea -da:com.Blah Main</td>

<td>all but one class named <tt>Blah</tt></td>
</tr>
</table>
<br>

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<div class='topic-section'>See Also :</div>
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  <a href='TopicActionc981-2.html?Id=64'>Conditional compile</a> <br>
 
  
  <a href='TopicAction3af3-2.html?Id=130'>Pass all pertinent data to exceptions</a> <br>
 
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